1. Field of the Invention
This invention relates to an apparatus for recording a digital signal on a magnetic tape. Also, this invention relates to an apparatus for reproducing a digital signal from a magnetic tape. In addition, this invention relates to a method of recording a digital signal on a magnetic tape. Furthermore, this invention relates to a method of reproducing a digital signal from a magnetic tape.
2. Description of the Related Art
A typical digital VTR (video tape recorder) divides a digital signal into a sequence of data blocks, and records the digital signal on a magnetic tape data-block by data-block. During a playback mode of operation, the typical digital VTR reproduces the digital signal from the magnetic tape.
There is a prior-art digital-signal recording and reproducing apparatus of a helical scan type which includes two magnetic heads having different azimuths respectively and mounted on a rotary drum. The two magnetic heads are diametrically opposed to each other. A magnetic tape is wrapped around the outer circumferential surface of the rotary drum along a part of a helix through an angular range of about 180 degrees. During a recording mode of operation, the prior-art apparatus divides a digital signal into a sequence of data blocks. The magnetic heads record the digital signal on the magnetic tape data-block by data-block while the magnetic tape is driven at a constant speed. During a playback mode of operation, the magnetic heads reproduce the digital signal from the magnetic tape while the magnetic tape is driven at the constant speed.
The mode of operation of the prior-art apparatus is changed depending on the drive speed of the magnetic tape. During a standard recording mode and a standard playback mode of operation, the magnetic tape is driven at a predetermined standard speed. The prior-art apparatus which operates in the standard recording mode can continuously record a digital signal having a data rate of 14.1 Mbps on a 120-minute S-VHS (trademark) tape for 240 minutes.
For a digital signal having a data rate lower than 14.1 Mbps, it is known to intermittently implement recording as follows. The tape drive speed is set to 1/N times the standard speed while the recording of the digital signal on the magnetic tape is implemented once in every N/2 turns (revolutions) of the rotary drum. Here, xe2x80x9cNxe2x80x9d denotes an odd integer greater than xe2x80x9c1xe2x80x9d. The recording rate provided by the intermittent recording is equal to 1/N times that by the standard recording. The longest record time provided by the intermittent recording is equal to N times that by the standard recording.
The prior-art apparatus includes servo control circuits for the rotary drum and the magnetic tape respectively. Operation of the servo control circuits, which occurs during the standard recording mode or the standard playback mode of operation of the prior-art apparatus, is disclosed. On the other hand, operation of the servo control circuits, which occurs during the intermittent recording, is unknown.
There is a conventional time-lapse VTR which intermittently implements recording of an analog signal for a long time. In the time-lapse VTR, a magnetic tape is driven at a low speed or driven intermittently. In addition, a rotary head intermittently records the analog signal on the magnetic tape.
It is a first object of this invention to provide an improved magnetic recording apparatus.
It is a second object of this invention to provide an improved magnetic reproducing apparatus.
It is a third object of this invention to provide an improved method of magnetic recording.
It is a fourth object of this invention to provide an improved method of magnetic reproduction.
A first aspect of this invention provides a magnetic recording apparatus having a rotary drum and being able to operate in a long time recording mode. The apparatus comprises first and second magnetic heads provided on the rotary drum and alternately scanning a magnetic tape, the first and second magnetic heads being different from each other in azimuth angle; first means for feeding a digital information signal to the first magnetic head and enabling the digital information signal to be recorded on the magnetic tape via the first magnetic head while the first magnetic head is scanning the magnetic tape in the long time recording mode of operation where the magnetic tape is driven at a speed equal to a predetermined standard speed multiplied by 1/N, and N denotes a predetermined integer equal to or greater than 2; second means for feeding the digital information signal to the second magnetic head and enabling the digital information signal to be recorded on the magnetic tape via the second magnetic head while the second magnetic head is scanning the magnetic tape in the long time recording mode of operation; third means for, in the long time recording mode of operation, inhibiting the feed of the digital information signal to the first magnetic head and the second magnetic head by the first means and the second means during an (Nxe2x88x921)/2 turn of the rotary drum after either the feed of the digital information signal to the first magnetic head by the first means or the feed of the digital information signal to the second magnetic head by the second means; a third magnetic head being fixed and scanning the magnetic tape; and fourth means for generating a control pulse signal, and feeding the generated control pulse signal to the third magnetic head and enabling the generated control pulse signal to be recorded on the magnetic tape via the third magnetic head, the generated control pulse signal having a period corresponding to one turn of the rotary drum, the generated control pulse signal having a duty cycle depending on timings at which the first and second magnetic heads record the digital information signal on the magnetic tape.
A second aspect of this invention is based on the first aspect thereof, and provides a magnetic recording apparatus wherein the fourth means comprises means for setting the duty cycle of the control pulse signal to a first predetermined value during one turn of the rotary drum immediately before the first magnetic head scans the magnetic tape and the digital information signal is fed to the first magnetic head by the first means, and means for setting the duty cycle of the control pulse signal to a second predetermined value during other time intervals, the second predetermined value being different from the first predetermined value.
A third aspect of this invention is based on the first aspect thereof, and provides a magnetic recording apparatus further comprising fifth means for reproducing the control pulse signal from the magnetic tape via the third magnetic head; sixth means for detecting a duty cycle of the reproduced control pulse signal; seventh means for deciding a recording track sequence on the basis of the detected duty cycle; and eighth means for implementing assemble recording on the magnetic tape via the first and second magnetic heads while maintaining the decided recording track sequence.
A fourth aspect of this invention provides an apparatus for reproducing a digital information signal from a magnetic tape in a long time playback mode of operation. The apparatus has a rotary drum and generates a drum pulse signal synchronous with rotation of the rotary drum. The magnetic tape stores a control pulse signal having a period corresponding to one turn of the rotary drum. The control pulse signal has a duty cycle depending on timings at which two magnetic heads of different azimuths record the digital information signal on the magnetic tape. The apparatus comprises first and second magnetic heads provided on the rotary drum and alternately scanning the magnetic tape to reproduce the digital information signal therefrom, the first and second magnetic heads being different from each other in azimuth angle; first means for reproducing the control pulse signal from the magnetic tape; second means for detecting the duty cycle of the control pulse signal reproduced by the first means; third means for deciding time intervals during which the digital information signal is effectively reproduced from the magnetic tape by the first and second magnetic heads in response to the duty cycle detected by the second means and the drum pulse signal, and for generating a reproduction control signal representing the decided time intervals; a reproducing circuit for processing output signals of the first and second magnetic heads; and fourth means for controlling the reproducing circuit in response to the reproduction control signal generated by the third means.
A fifth aspect of this invention is based on the fourth aspect thereof, and provides an apparatus wherein the third means comprises first sub means for deciding whether or not the detected duty cycle corresponds to the first magnetic head; a synchronous counter for counting up every leading edge in the drum pulse signal in cases where the first sub means decides that the detected duty cycle does not correspond to the first magnetic head, the synchronous counter being reset by a leading edge in the drum pulse signal in cases where the first sub means decides that the detected duty cycle corresponds to the first magnetic head; and second sub means for generating the reproduction control signal in response to an output signal of the synchronous counter and the drum pulse signal.
A sixth aspect of this invention provides a method of magnetic recording in modes of operation which include a long time recording mode of operation. The method comprises the steps of 1) feeding a digital information signal to a first magnetic head and enabling the digital information signal to be recorded on a magnetic tape via the first magnetic head while the first magnetic head is scanning the magnetic tape in the long time recording mode of operation where the magnetic tape is driven at a speed equal to a predetermined standard speed multiplied by 1/N, and N denotes a predetermined integer equal to or greater than 2; 2) feeding the digital information signal to a second magnetic head and enabling the digital information signal to be recorded on the magnetic tape via the second magnetic head while the second magnetic head is scanning the magnetic tape in the long time recording mode of operation, wherein the first and second magnetic heads are provided on a rotary drum and alternately scan the magnetic tape, and the first and second magnetic heads are different from each other in azimuth angle; 3) in the long time recording mode of operation, inhibiting the feed of the digital information signal to the first magnetic head and the second magnetic head by the step 1) and the step 2) during an (Nxe2x88x921)/2 turn of the rotary drum after either the feed of the digital information signal to the first magnetic head by the step 1) or the feed of the digital information signal to the second magnetic head by the step 2); and 4) generating a control pulse signal, and feeding the generated control pulse signal to a third magnetic head and enabling the generated control pulse signal to be recorded on the magnetic tape via the third magnetic head, the third magnetic tape being fixed and scanning the magnetic tape, the generated control pulse signal having a period corresponding to one turn of the rotary drum, the generated control pulse signal having a duty cycle depending on timings at which the first and second magnetic heads record the digital information signal on the magnetic tape.
A seventh aspect of this invention provides a method of reproducing a digital information signal from a magnetic tape in a long time playback mode of operation. The method generates a drum pulse signal synchronous with rotation of a rotary drum. The magnetic tape stores a control pulse signal having a period corresponding to one turn of the rotary drum. The control pulse signal has a duty cycle depending on timings at which two magnetic heads of different azimuths record the digital information signal on the magnetic tape. The method comprises the steps of 1) reproducing the control pulse signal from the magnetic tape; 2) detecting the duty cycle of the control pulse signal reproduced by the step 1); 3) deciding time intervals during which the digital information signal is effectively reproduced from the magnetic tape by first and second magnetic heads in response to the duty cycle detected by the step 2) and the drum pulse signal, and generating a reproduction control signal representing the decided time intervals, wherein the first and second magnetic heads are provided on the rotary drum and alternately scan the magnetic tape to reproduce the digital information signal therefrom, and the first and second magnetic heads are different from each other in azimuth angle; 4) processing output signals of the first and second magnetic heads; and 5) controlling the processing by the step 4) in response to the reproduction control signal generated by the step 3).